do i go according to the conception date or the first day of my last period to figure out a due date?

Question

I know 100% sure the day I concieved (5/11), it was the only act in the month. When I count 40 weeks from that day I get 2/15. I have done a few of the calculators online they all come up 2/3. I have done the online calculator with both the conception date, and the fist day of my last period but is says the same. Does anyone know anything about due date calculations? It seems like they all are calculating 38 weeks instead of 40. Should I just go with my calculations? I know it couldnt be any other day.

Answer 1

The reason they're all coming up the same is because if you use the conception date, then you would add 38 weeks, not 40.



The 40 week number is based upon a 28 day, or 4 week, cycle. The first two weeks you are not pregnant since you haven't even ovulated yet at that point. Since conception date looks at ovulation, which is usually about two weeks before your next period starts, you don't add in the weeks before ovulation.



Also, just because you had intercourse on the 11th doesn't mean that's the day you conceived. Sperm can live in the reproductive tract for up to 5 days (usually around 3), so it could have even been a few days later than that.



The most accurate way to get a due date is to have a transvaginal ultrasound at 8-10 weeks gestation. It will be accurate +/- 1 day.

Answer 2

Most due date calculators have you put in one or the other. Usually when you go to the doctors, they'll ask you the first day or your last period and give you a due date that way. Because they count those two weeks before actual conception as part of the 40 weeks.

Answer 3

They are probably coming up with the same date cause conception happens antime within the two weeks after the frst day of your last period, and a due date is just a round a bout time frame cause you can have the baby any time from 38 weeks to even after 40 weeks. Whenever you go to the doctor though, you will probably get an ultrasound to measure the baby and see exactly how far along you are, and get a better due date.

My due date changed about three times, I was pregnant last year and I was due in November, first when going off my period date it was November 3rd, then I had an ultasound to measure the baby and that gave me a due date of November 11th, then I changed doctors, cause I wasn't liking mine too much, she gave me another ultrasound and that gave me a du date of November 8th, I had her November 2nd after all, so like I said before it is just a round about date to expect.

Good luck and congratulations!!!

Answer 4

Doctors use date of lmp. When you calculate this way the first two weeks you are not actually pregnant yet. Most people are not sure their exact date of conception so this is an effective method. SO... take the first day of your last period add 7 days then subtract 3 months. EX: my lmp was 2/11 + 7 = 2/18- 3 months = November 18. I am due 11/18/07.

Answer 5

In my book it states that a pregnancy last 265 days from conception and 280 days from the first day of your last menstrual period, assuming a 28-day cycle. The rule for calculating your due date is to subtract 3 months and add 7 days.. For example if the first day of your last menstrual was September 7, then your due date would be June 14. Deciding how far along you are can be confusing because pregnancy duration is calculated in Lunar months of 28 day cycles as opposed to calendar months of 31 days.. Consequently, pregnancy last 10 lunar months (40 weeks) or 9 calendar months.. I do hope this helps you understand a little bit about the due dates you are getting. Best of Luck and Congratulations...

Answer 6

Not everybody know the date of conception (more than one act, hehe) so the formula is based on first day of period. Whilst the doc may tell you one date based on first day of period but because you knew your exact date of conception you can keep in mind your own due date. It really doesn't matter as by certain weeks, the baby can come out anytime. That's why one normally gets the answer "Anytime" when one ask a heavily pregnant lady when is her due date.

Answer 7

Eh, either way isn't all that accurate. However, using your LMP and a 28 day cycle is a little more accurate on predicting the date of conception, especially if you did not have an ultrasound in the first 10-12 weeks. Nearly all babies grow at the same rate in the first 10-12 weeks, so it is pretty easy and accurate to determine the approximate conception date that way.

Answer 8

You're supposed to go from the day of your last period although sometimes that can be off depending on the length of your normal cycles. They predicted mine according to my last period, but then when I got my first ultrasound, based on the size of the baby they determined that my due date would be one week later. It is confusing, but at least you know in general when to expect your baby... it's not like they ever come right on the due date anyway. Good luck!

Answer 9

Your due date is based on the length of an average pregnancy, which is 280 days, or 40 weeks from the first day of your last period.

Answer 10

I forgot the formula- but go with the online calculations...you are suppossed to count fowards then back- or the other way around. This is the website I used and it was right on to the day! Oh...and you don't start from your date of conception...but the date in which you had your last period.



http://www.marchofdimes.com/pnhec/1808_1892.asp

Answer 11

your due date is 40 weeks from the first day of your last period; so yes, technically, going from conception it is only 38 weeks. i think it just makes it easier to figure out, b/c most women know their last period, not everyone knows the day of conception. congrats!! and good luck!

Answer 12

You should go by the doctors figuring, which is the first day of your last period, that way you and your doctor are on the same page. The doctors go by that last day because even of you think you know the exact day you concieved, you could be off by a day or two.



Congratulations!

Answer 13

the doctors count 40 weeks from your last period, so it should be due date 2 february. and from your conception date you count 38 weeks.

Answer 14

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Enjoying the feeling of motherhood and raising a family would surely be a couple’s dream. Some get it naturally, while for some others things don’t seem to work as they desire. These reasons which stop a women from conceiving can be due to either physical reasons or truly physiological.

Answer 15

you need to use the date of your last period. The date you actually had the sex really has nothing to do with it, it only has to do with whether you were ovulating somewhere during that time.

Answer 16

no, you go by the first day of your last prd. - go to any online due date calculator

Answer 17

first day of your last period